Steam turbine rotor cooling



Dec. 13, 1966 R. E. BRANDON STEAM TURBINE ROTOR COOLING Filed Feb. 15, 1965 INVENTOR RONALD E. BRANDON,

HIS ATTORNEY.

United States Patent 3,291,447 STEAM TURBINE ROTOR COOLING Ronald E. Brandon, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Feb. 15, 1965, Ser. No. 432,741 6 Claims. (Cl. 253-391) ABSTRACT: LEAKAGE STEAM PASSING THROUGH TURBINE WHEEL BALANCE HOLES IS FORCED FROM SPACE BETWEEN WHEEL AND STATIONARY DIAPHRAGM INTO WORKING STEAM PATH BY WORKING STEAM COLLECTED IN PASSAGE ON LEADING EDGE OF DOWN- STREAM STATIONARY BLADES.

This invention relates to a cooling arrangement for elastic fluid axial flow turbines. More particularly, the invention relates to an arrangement for reducing the possiblity of overheating or distorting the turbine parts with hot leakage fluid in the spaces between turbine wheels and sationary diaphragms.

In many types of elastic fluid turbines, leakage fluid from various sources may be significantly diiferent in temperature than the main steam flow. Similarly, fluid passing through the turbine at inner and outer boundaries of the annulus where fluid losses are greatest will become hotter than the fluid passing through the central portion of the flow path.

If these portions of flow are permitted to segregate, they may cause unequal and undesirable temperature distribution and distortion in stationary parts and higher than desirable temperature in rotating parts.

For example, fluid leaking through labyrinth packing between stages of multiple stage turbines does no useful work within the stage and may be significantly hotter than the working steam which is passing through the nozzles and buckets. If this same fluid leaks through the labyrinth packing in the following stages, the temperature difference between it and the working fluid will grow ever greater.

The result may be unequal heat or overheating of the Wheel spaces between the Wheels and diaphragms. This overheating can cause diaphragm distortion, extra leak age and rubbing, rotor bowing, and other undesirable phenomena.

It was proposed in U. S. Patent 2,552,239, issued to G. B. Warren on May 8, 1951 and assigned to the assignee of the present application, to introduce supplementary cooling steam from an outside source Which flowed alternately through the turbine wheel balance holes and around the diaphragm packing between a series of chambers isolated from the Working fluid path by rotating seals. This arrangement required close control of the cooling steam flow and entailed added expense through the rotating seals and external piping required.

Where there is no provision made for introducing a separate source of cool steam to flow through the balance holes and around the diaphragm seal, it has been found that this inherent leakage flow increases in relative temperature, both because energy is not being extracted by expansion through a working stage of blades and because it is heated by frictional rotation loss. The efiiciency of the turbine would benefit if the energy in this hot leakage gas could be returned to the working steam path.

Accordingly, one object of the present invention is to provide an arrangement for reducing overheating of the inner wheel and diaphragm spaces of a turbine, as well as reducing energy losses in the flow of leakage fluid.

Another object of the invention is to provide an improved means for providing cooling fluid for the s pace between turbine wheel and diaphragm webs in an axial flow turbine.

Another object of the invention is to provide an im proved structure for recovering energy in the motive fluid which escapes through the balance holes of steam turbine wheels.

Briefly stated, the invention is practiced by providing collecting passages in the Working steam path at a convenient location, such as on the leading edge of a downstream nozzle partition, and providing passages to conduct this cooler steam to the space between the diaphragm and an upstream turbine wheel. A portion of this cooling steam replenishes the inherent leakage flow around the labyrinth seal between diaphragm and shaft. The other portion of the steam serves to deflect hot leakage steam outward into the working steam path Where its energy can be recovered.

For a better understanding of this invention, reference is made to the accompanying drawing in which:

FIG. 1 is a horizontal elevation drawing, partly in section, of a multistage axial flow steam turbine, showing portions of two diaphragms and two turbine wheels, and

FIG. 2 is a cross-sectional view of a stationary nozzle partition, taken along lines IIII of FIG. 1.

Referring now to FIG. 1 of the drawing, the turbine includes a casing, a portion of which is shown generally at 1, and a rotor, a portion of which is shown generally at 2. Only two steam turbine stages are shown in the drawing, since it will be understood by those skilled in the art that the remainder of the turbine necessarily includes means for introducing steam at the high pressure end through suitable inlet passages, and that the turbine also includes means for either an exhaust hood or for an outlet passage conducting the steam to another turbine section.

The turbine rotor 2 includes an inner shaft portion 3 and a series of turbine wheels such as 4, 5 which may be formed integrally with shaft 3 from a single forging. Secured to the circuferences of turbine wheels 4, 5 are a series of spaced buckets or blades 6, 7 surrounded by shroud bands 8.

Stationary diaphragms 9, 10 are supported in casing 1 and associated with wheels 4, 5 respectively for directing the working elastic fluid, such as steam, to the buckets. These diaphragms are in the form of annular disk members and include solid inner webs 11, 12 and rings of circumferentially spaced blades or nozzle partitions 13, 14 forming nozzle passages between them.

Arranged around the central openings in the diaphragms and cooperating with shaft 3 are labyrinth packings 15 which limit the flow of steam through the clearance spaces between the shaft 3 and the respective diaphragms.

In order to prevent excessive axial thrust forces on rotor 2 due to the pressure differences on either side of the turbine Wheels, pressure balancing holes such as 16, 17 are often provided through the web portions of the respective wheels. As will be explained later, however, the invention is also useful in turbine stages which do not employ balance holes.

Between diaphragm web 11 and wheel 4, a wheel space chamber 18 is isolated from the working steam path by means of a rotating seal member 19 and a spill band 20. On the other side of turbine wheel 4, a wheel space chamber 21 is relatively open to the working steam path through the annular passage 22. Diaphragm web 12 includes an intengral axially projecting lip 23 which is positioned opposite an outlet 16a of balance port 16.

Essentially the sarne structure as that described is repeated from one stage to the next along the turbine. For example, repetition of elements comparable to those just described can be seen in the form of: Wheel space 24 isolated from the working fluid path by seal 25 so 3 that leakage fluid passes through balance hole 17 against the portion of deflecting lip seen at 26.

A means for introducing cooling steam into wheel space 21 is provided by means of collecting slots 27 in the leading edges of selected nozzle partitions 14. Slots 27 interconnect with radial passages such as 28 through the partition or blade itself which, in turn, interconnect with larger inwardly directed passages 29 in the web 12 of the diaphragm. Slot 27 and interconnected passages 28, 29 act as a collection and diffusing conduit to collect working steam after it has been expanded through (and therefore cooled by) the upstream bucket 6 and for directing this cooler steam inwardly to the wheel space 21. It should be particularly noted that since the steam arriving at space 21 has been expanded through turbine bucket 6, it will be cooler than the higher energy steam in the upstream wheel space chamber 18 which normally would pass through balance holes 16 into chamber 21.

Reference to FIG. 2 of the drawing, the top view of blade 14 illustrates a suitable means for providing the collecting slot 27, wherein it is seen that this is simply milled into the leading edge of nozzle blade 14 so as to intersect a hole 28 slanting upward from the base of the nozzle blade.

The operation of the invention will be apparent from the following descripition. Leakage steam is present in wheel space 18 from a higher pressure stage and is prevented from escaping to the steam path by seal 19. This leakage steam therefore passes through the balance holes 16 and from there against the lip 23 where it is partially deflected outward into the working steam path. To assist in preventing this hotter leakage steam from entering wheel space 21, cooler working steam is collected in slot 27 and passes radially inward through passages 28, 29 as indicated by the arrows. Flow is partially forced by the conversion of velocity head of the working steam to static pressure and induced by the pumping effect of wheel 4.

The collected steam issuing from passage 29 is divided into two portions. A portion of this flow passes radially outward through the annular passage 22 and, in so doing further deflects the hot leakage steam issuing from balance hole outlets 16a into the working fluid path. The other portion of the cool steam flows radially inward, and past the layb-yrinth packing 15 into wheel space 24. In wheel space 24 this leakage steam is now hotter, relatively speaking, than steam which has been expanded through the next stage of turbine blades 7, and the cycle is repeated.

It should be observed that for many stages built without balance holes, this cooling system is equally useful. Such constructions normally eliminate balance holes 16 as well as seals 19 so that wheel space 18 is open to the main steam path. Leakage past the first packing 15, in this case, is supposed to join the working flow path. Experience has shown that it still does no useful work passing through rotating blades 6 and furthermore remains generally segregated so as to enter space 21, drawn there as the flow required by the subsequent labyrinth packing 15.

Cool flow discharging from holes 29 can again prevent this hot flow from another cycle of leakage and greater temperature difference with the working fluid in the same way described above for stages with balance holes.

The foregoing system aids greatly in reducing diaphragm distortions, since, at each stage, the cooling fluid for the inner diaphragm is collected at that particular location of the turbine. Therefore, there is no necessity for controlling cooling from an external source, this being automatically achieved with the arrangement described.

It will also be observed that the flow rate of cooling steam which flows past each packing approximates the flow rate of leakage steam passing the preceding turbine wheel. Therefore, at each stage, leakage flow is replenished with cooler steam, while the hotter steam is returned to the cycle to add to the efiiciency of the turbine.

Various other modifications of the invention may occur to those skilled in the art, and it is desired to secure, by the appended claims, all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent to the United States is:

1. In a multistage axial flow elastic fluid turbine the combination of:

a turbine wheel portion extending radially from a rotatable shaft portion, said wheel portion having a plurality of turbine buckets on its periphery,

a stationary annular diaphragm member having a plurality of nozzle partitions thereon disposed to receive fluid from said :buckets, said diaphragm member also including packing means closely surrounding the shaft portion, and

means defining a cooling fluid passage having an inlet defined in the leading edge of a selected nozzle partition of said diaphragm so arranged as to collect elastic fluid after it has passed through said buckets and having an outlet discharging into the space between said wheel portion and said diaphragm member, whereby a portion of the collected fluid flows between the packing means and the shaft portion after having been cooled by passing through the preceding turbine buckets.

2. In a multistage axial flow elastic fluid turbine, the

combination of:

a turbine wheel portion extending radially from a rotatable shaft portion, said wheel portion having a plurality of turbine buckets on its periphery and also defining balance passages therethrough having outlets,

a stationary annular diaphragm member having a plurality of nozzle partitions thereon disposed to receive fluid from said buckets, said diaphragm member also including packing means closely surrounding the shaft portion, and

means defining a cooling fluid passage having an inlet disposed on said nozzle partitions to collect elastic fluid after it has passed through said buckets and arranged to discharge fluid generally toward said turbine wheel portion between the packing means and said balance passage outlets, whereby a portion of the collected fluid diverts fluid passing through the balance passages radially outward while the remainder of the collected fluid flows between the packing means and the shaft portion.

3. The combination according to claim 2, wherein said diaphragm member defines an annular lip disposed adjacent said pressure balance passage outlets and arranged to deflect fluid passing through said balance passages radially outward.

4. The combination according to claim 2 wherein each of said cooling fluid passage inlets comprises a collecting slot defined in the lea-ding edge of selected nozzle partitions on the diaphragm.

5. In a multistage axial flow elastic fluid turbine, the combination of:

a rotor having a shaft with a plurality of axially spaced turbine wheels, each with a circumferential row of buckets for extracting energy [from working fluid and defining at least one pressure balancing passage through the wheel having an outlet discharging leakage fluid at a location radially inward from the buckets,

a plurality of nozzle diaphragms disposed in the spaces between the respective turbine wheels and each having a plurality of circumferentially spaced nozzle partitions and also having packing means surrounding the shaft and defining a restricted fluid flow path from one side of the diaphragm to the other, and

means defining a plurality of cooling fluid passages each having an inlet disposed in the leading edge of a nozzle partition of .a selected diaphragm and discharging on the high pressure side of said selected diaphragm between the packing means of that diaphragm and the balance passage outlets of the preceding turbine wheel.

6. The combination according to claim 5 wherein each of said diaphragms defines an annular lip disposed adjacent the outlet of the pressure balance passage of the said cooling fluid in deflecting leakage fluid into the Working fluid path.

References Cited by the Examiner UNITED STATES PATENTS 1,819,864 8/1931 Bloomberg. 2,919,891 1/1960 Oliver 253-3915 X MARTIN P. SCHWADRON, Primary Examiner.

preceding turbine Wheel and arranged to cooperate with 10 E. POWELL, Assistant Examiner- 

1. IN A MULTISTAGE AXIAL FLOW ELASTIC FLUID TURBINE THE COMBINATION OF: A TURBINE WHEEL PORTION EXTENDING RADIALLY FROM A ROTATABLE SHAFT PORTION, SAID WHEEL PORTION HAVING A PLURALITY OF TURBINE BUCKETS ON ITS PERIPHERY, A STATIONARY ANNULAR DIAPHRAGM MEMBER HAVING A PLURALITY OF NOZZLE PARTITIONS THEREON DISPOSED TO RECEIVE FLUID FROM SAID BUCKETS, SAID DIAPHRAGM MEMBER ALSO INCLUDING PACKING MEANS CLOSELY SURROUNDING THE SHART PORTION, AND MEANS DEFINING A COOLING FLUID HAVING AN INLET DEFINED IN THE LEADING EDGE OF A SELECTED NOZZLE PARTITION OF SAID DIAPHRAGM SO ARRANGED AS TO COLLECT ELASTIC FLUID AFTER IT HAS PASSED THROUGH SAID BUCKETS AND HAVING AN OUTLET DISCHARGING INTO THE SPACE BETWEEN SAID WHEEL PORTION AND SAID DIAPHRAGM MEMBER, WHEREBY A PORTION OF THE COLLECTED FLUID FLOWS BETWEEN THE PACKING MEANS AND THE SHAFT PORTION AFTER HAVING BEEN COOLED BY PASSING THROUGH THE PRECEDING TURBINE BUCKETS. 